This invention relates to a four-bar trailer hitch.
Heretofore, there have been numerous proposals for four-bar trailer hitches, and it has been recognized in the art that these can provide certain advantages in the stability and control of articulated road vehicles. One reason for this is that, by providing two forwardly convergent arms, the instantaneous center of rotation, referred to in the art as the ICR, is moved forwardly toward the vicinity of the rear axle of the tow vehicle. The following United States patents disclose four-bar trailer hitches which are symmetrical with respect to the centerlines of the towing and towed vehicles:
Minter: U.S. Pat. No. 2,444,944 PA0 Gallatin: U.S. Pat No. 3,790,190 PA0 Miller: U.S. Pat. No. 3,787,068 PA0 Hinkley: U.S. Pat. No. 4,019,754 PA0 Sallis: U.S. Pat. No 4,106,794.
Darvill's British specification No. 556,290 discloses a four-bar hitch which is asymmetrical with respect to the vehicles, but its purpose is for pulling farm machinery such as reapers which are relatively light, slow and are turned in only one direction. The off-center link of the Darvill hitch is shifted between the right and left side of the mechanism, depending on which direction the tractor will turn when working a field.
One object of the present invention is to provide a four-bar hitch which is more readily adaptable to existing vehicle structures than the four-bar hitches of symmetrical construction, inasmuch as the invention may utilize existing coupling structures which are located on the centerlines of the respective vehicles. Another object of the invention is to provide a four-bar hitch which is lighter and less expensive than many four-bar hitches which have been proposed, this attribute being due in part to the fact that the second link which performs a steering function has strength requirements which are less than the strength required of both links in a symmetrical four-bar hitch.
Another object of the invention is to provide a four-bar hitch which is more easily hooked up between the vehicles than most previous designs which have been proposed or produced.
Still another object is to provide a hitch system which, under extreme maneuvering conditions, makes it possible to make very sharp turning angles without interference between the two links of the hitch.
A further object of the invention is to provide a hitch which has a laterally shiftable coupling which enables the vehicle operator conveniently to convert the hitch from a four-bar mode of operation at highway speeds to a simpler arrangement more closely resembling a single pivot for maneuvering and driving the vehicle at lower speeds where stability is of less concern.
One embodiment of the invention has the further object of providing a supplemental vertical asymmetrical four-bar linkage which performs a load transferring function while permitting the vehicles to pitch relative to each other.
Other features and attributes of the invention will be appreciated by those skilled in the art after reading the remainder of this specification.